Malignant tachyarrhythmia, for example, ventricular fibrillation, is an uncoordinated contraction of the cardiac muscle of the ventricles in the heart, and is the most commonly identified arrhythmia in cardiac arrest patients. If this arrhythmia continues for more than a few seconds, it may result in cardiogenic shock and cessation of effective blood circulation. As a consequence, sudden cardiac death (SCD) may result in a matter of minutes.
In patients at high risk of ventricular fibrillation, the use of an implantable cardioverter defibrillator (ICD) system has been shown to be beneficial at preventing SCD. An ICD system includes an ICD, which is a battery powered electrical shock device, that may include an electrical housing electrode (sometimes referred to as a can electrode), that is coupled to one or more electrical lead wires placed within the heart. If an arrhythmia is sensed, the ICD may send a pulse via the electrical lead wires to shock the heart and restore its normal rhythm. Owing to the inherent surgical risks in attaching and replacing electrical leads directly within or on the heart, subcutaneous ICD systems have been devised to provide shocks to the heart without placing electrical lead wires within the heart or attaching electrical wires directly to the heart.
Subcutaneous ICD systems have been devised to deliver shocks to the heart by the use of a defibrillation lead placed subcutaneously on the torso. However, the subcutaneous ICD systems may require an output of around 80 Joules (J) of energy to provide effective defibrillation therapy. As a result, subcutaneous ICDs may require larger batteries and more storage capacitors than transvenous ICDs. As such, the subcutaneous ICDs are generally larger in size than transvenous ICDs. The large size of the subcutaneous ICD may compromise patient comfort, decrease system longevity and/or increase cost of the system. In addition, conventional subcutaneous ICD systems are incapable of delivering anti-tachycardia pacing (ATP) without extreme discomfort to the patient, which is a standard therapy in transvenous ICDs to terminate lethal tachyarrhythmias without providing a shock.